Spring or autumn reseeding

Published 14 March 14

If you are thinking about reseeding this spring, whether out of necessity due to flood damage or as a management decisions, Piers Badnell, DairyCo technical extension officer, looks at the issues surrounding spring and autumn reseeding

Reseeding has clear economic benefits but does incur costs and can put valuable grazing or silage ground out of production for a while. Ensuring you have an accurate picture of which fields are underperforming (link to article on range of field performances FfK Aug 13) in terms of grass production is crucial. The only way to do this is by measuring what is harvested in that field either by the cows or by what goes in the silage pit.

  • If a field is under performing, is there something you can do about it without reseeding?
  • Are pH or P&K levels causing problems? 
  • Is the soil healthy, is there healthy worm activity, can you see plenty of worm casts?
  • Are there signs of healthy flora and fauna?
  • Do dung pats disappear quickly as the soil life devours them or do they remain for protracted periods of time?
  • How well do the drains work in the field?
  • Is there a soil structure problem? Has the ground become compacted (link to article on soil compaction FfK Oct 12)?
  • In which case will slitting or sward lifting help to rectify soil structure problems and increase production?


If you have investigated other causes for a reduction in pasture performance, reseeding may be the solution.

Recent Milkbench+ analysis shows cost of production as the biggest driver of profit in dairy farming businesses. Reducing costs of production by increasing forage quality and quantity can make a huge difference to the bottom line. One of the ways to help you reach this goal is by having a structure reseeding policy.

From the first day a new ley is established there is a continual decline in the percentage of sown species as weed grasses and broad leaved weeds move into the sward. Even under good management, it is likely that after six years a medium term ley based around intermediate perennials could contain less than 60% ryegrass.

The impact of declining ryegrass content is a drop in both yield and quality. A young perennial ryegrass ley should yield well in excess of 10t DM/ha/yr in the first few years of its life – and if managed correctly should maintain quality above 11.5 ME and 20% crude protein.

Much of this yield and quality is driven by a high response to applied nutrients; for every kg of nitrogen applied (from bag/slurry or clover) you could see a 25kg DM response from a young vigorous sward at peak growing time.  With this level of response, grass is cheap forage.






Old leys may struggle to produce 6t DM/ha/yr and quite often because of poor response rates they may need greater nutrient inputs to achieve even that. The net result is less, poorer quality and more expensive grass.

There are two key times to look at reseeding in Great Britain, spring (April) and autumn (August and September), in order to ensure the best results.

Some farmers who were not planning on reseeding this spring may be faced with a different set of circumstances after prolonged flooding this winter (link to flooding article FfK Feb 14). Below are a series of factors to consider for both reseeding options.

 Spring reseeding (April)


  • No heading in first season for perennial ryegrass
  • Opportunity to hit weeds before they get established. As grass is actively growing it can better outcompete weed species
  • Minimal impact on grazing. Reseeding at the time of maximum grass growth may well mean you are not short of grazing elsewhere on the farm, so can afford to have that areas out of production
  • Timeliness – an early autumn is not creeping up on you putting the reseed in jeopardy
  • The probability of a good take of seeds in ideal spring growing conditions
  • If spring reseeding conditions turn out to be disastrous you have the opportunity of try again in autumn and don’t have to wait another year.



  • Loosing peak growth. By taking a field out at this time you are losing grass production at its highest peak  
  • The soil in spring reseeded areas might not have time to settle before they will need to carry stock
  • If the field hasn’t been ploughed before reseeding there may be competition from old grasses
  • If you don’t get good seed take, weeds have ideal growing conditions and can come to dominate sward.




  • The seedbed has time to settle over the winter and will not be damaged by carrying stock in the spring
  • Good seed take if reseeding is done in time and the autumn has good growing conditions
  • Less impact on grazing stock as no land is taken out of production during peak growth times
  • Good weed control, if done early and you can still hit weeds when actively growing.



  • If you reseed too late in the autumn you may find weed growth stronger and outcompeting grass.  You may have spent a lot of money on reseeding  only to have open swards colonised by meadow grass and chickweed
  • If autumn conditions come early reseeds will suffer
  • You run the risk of poor seed take at this time of year
  • The risk of weed ingression
  • Grass plants will head in the first season, with an impact on quality.


For further information on reseeding, there are DairyCo and British Grassland Society Factsheets (link).